(This article is a supporting part of our ongoing testing of low-light camera metering reliability)
The Canon M5 first fails to compensate at least 2/3 stop for a 1 stop decrease in light at EV-2.3, which is approximately equivalent to the light level provided by a full moon. At scenes darker than EV-3.8, its images are over one stop darker than those auto-metered at EV0. Compared to other cameras, the metering of the M5 gives a “last gasp” at about EV-2, producing a brighter-than-normal image, before completely giving up beyond that. The manufacturer reports that its metering limit is “EV 1 (at room temperature, ISO 100),” which is significantly brighter than what we measure.
Unlike Sony cameras, the Canon M5 does not stop down the lens to the user-set aperture at all times–only when taking a photo. In other words, if you are using an f/1.4 lens but have the camera set to f/4 for improved sharpness, the lens stays at f/1.4 until you click the photo. Therefore your metering and autofocus benefit from using a fast lens, even when it is set to a high f-number.
The Canon M5 has no options for when to increase the ISO vs shutter speed in Auto ISO mode. The maximum ISO can be limited, though.
The Canon M5 does not have the option of an all-electronic shutter, making it a poor choice for nighttime webcams which take a million photos per year. In auto-ISO mode, timelapse has the standard 1/3 stop flicker caused by settings changes.
The plot shown above was created using the usual EF-mount Rokinon 50mm f/1.4 adapted to Canon EF-M and set to f/2.8. The aperture-dependent metering phenomenon was tested with a Canon EF-M 22 f/2.
Integrating Sphere & Camera Metering Test Project